•Precise deposition of alumina support layers in microchannels with uniform thickness.•Adjustable support layer thickness through repeated inkjet printing.•Homogeneous distribution of Rh nanoparticles within the printed support layers.•Stable performance of Rh/Al2O3 catalyst coating in methane steam reforming for >60 h.

Inkjet printing technology was applied for the precise deposition of alumina nanoparticles in microchannels as a catalyst support layer. Several alumina nanoparticle containing inks were prepared and tested for inkjet printability. It could be shown that additives such as ethylene glycol and polyethylene glycol are needed for aqueous inks up to a concentration of 50 wt.% for continuous drop generation. The printing was conducted both in semicircular and rectangular microchannels. The coating thickness was controlled by repetitive printing of each channel, and the generated layers were uniform in thickness throughout the microchannel foil. The printed alumina layers were impregnated with rhodium nitrate after calcination. A high metal loading of 15 wt.% was applied to enable a high reaction rate per coated area despite the low thickness of the layer, and the catalytic activity was demonstrated for methane steam reforming (MSR). The prepared catalyst layers were highly active, and conversions exceeding 98% were obtained at 973 K and a W/F (catalyst weight/CH4 feed rate) ratio of 19.7 (kgcat s)/molCH419.7 (kgcat s)/molCH4.